fast-and-clean

Arguments: &body body

This is a direct replacement for (excl::fast (atomically
...)) when that was used to warn of a loss of expected
efficiency (fast and atomically were not exported or documented). It
will provide the same warnings and the same generated code that the
old combination gave. The new macro exists to provide
self-documentation of the intended use.

Lisp interrupts and gc requests are honored only at certain points in
Lisp code. The compiler verifies that during the execution
of body there are no checks for Lisp
interrupts or gc requests. If the compiler detects that this
assumption may be violated, an error is signaled at compile time.
This form is similar in effect to with-delayed-interrupts, but no explicit
interrupt or gc check is made; an interrupt or gc check will occur at
the next function call or loop iteration.